JPH0118677B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for accelerating and decelerating an electric motor using a power conversion device, and in particular to an improved control of an electric motor that adjusts an acceleration/deceleration rate using a quantity related to acceleration/deceleration torque. Regarding equipment.

The present invention can be applied to any system in which a power conversion device and an electric motor are combined. For example, combinations include a DC Leonardo motor and a DC motor, a thyristor motor control device and a synchronous motor, a current source inverter and an induction motor, etc. The explanation below includes
Let's take the combination of a current source inverter and an induction motor as an example.

FIG. 1 shows a system to which the present invention is applied. In the figure, AC power supplied from an AC power source AC11 is converted into AC power having an arbitrary frequency via a current inverter 12, and is supplied to an induction motor IM13. The load device 14 is coupled to the rotor of the induction motor 13 and performs work, but for the sake of the following explanation, it has a square load characteristic (the load torque has a substantially square characteristic with respect to speed) like a fan or a blower. shall be taken as a thing. At this time, in order to simplify the explanation, static friction torque, mechanical loss, etc. at the time of startup are not considered. FIG. 2 shows a detailed circuit of the current source inverter 12. A rectifier 121 connected to the AC power supply 11 converts AC power into DC power, which is smoothed through a DC reactor 122 and then converted into AC power having an arbitrary frequency through an inverter circuit 123. When accelerating or decelerating the load device 14 using the above system, the circuit shown in FIG. 3 has generally been used as a control circuit. In the figure, the speed reference S1 given by the setting device 21 is
The V/F reference S2 is output by replacing the step change with a ramp function change. At this time, the setters 23 and 24 generate signals l1 and l2 for setting the rate of change during acceleration and deceleration, respectively. The voltage/frequency V/F reference S2 becomes a voltage reference v, which is compared and amplified with a voltage feedback signal obtained via a transformer 27 in a comparator 25 and a voltage control circuit 26 to obtain a current reference. This current reference is compared and amplified with a current feedback signal obtained via a current transformer 30 in a comparator 28 and a current control circuit 29, and becomes a phase reference. And this phase reference is
An ignition pulse for controlling the rectifier 121 is generated in a phase control circuit 32 in relation to the power supply phase obtained via the transformer 31 . On the other hand, the V/F reference S2 also serves as a frequency reference f, and generates a firing pulse for controlling the inverter circuit 123 via an oscillator 33 and a ring counter 34. Figure 4 shows input restriction means 2.
2 details are shown. In the same figure, the speed standard S
1 is passed through a resistor 51, and the output signal a of the integrating circuit is passed through a resistor 52 and then compared and amplified by an operational amplifier 53. If it is during acceleration, S ₁ >a, and if it is during deceleration, S ₁ <a, so the output signal b of the operational amplifier 53 has the (-) and (+) polarities, respectively. Output signal b is inverted by operational amplifier 56 with a gain determined by resistors 54 and 55, integrated by operational amplifier 59 with a time constant determined by resistor 57 and capacitor 58, and output signal a is can get. This output signal a is the absolute value conversion circuit 6
0, the V/F reference S2 is always at (+) potential. With the above integration circuit, limiters 61 and 62
The acceleration/deceleration time is determined by the limit value determined by . For example, during acceleration, the output signal b has (-) polarity, so the output signal b and the resistor 63,
+15V power supply and resistor 64, signal to set rate of change
The base potential of the limiter 61 is determined by the divided voltages of _l1 and the resistor 65, and when the output signal b reaches a certain (-) potential, the limiter 61 operates,
It moves so that the potential does not reach any more (-). The same is true during deceleration, and the output signal b and the resistors 66, -
The output signal b is kept at a certain (+) potential by the 15V power supply, the resistor 17 signal _l2 , and the voltage division of the resistor 68.

FIG. 5 shows the relationship between time t and V/F reference S2 when acceleration is performed using the input limiting circuit 22 described above. In the figure, if the signal _l1 that sets the rate of change is constant, the current flowing into the integrating circuit is constant, and exhibits uniform acceleration characteristics. FIG. 6 shows the load torque T _L and the generated torque T _M of the induction motor 13 when the vehicle is similarly accelerated. The acceleration torque Ta (shown with diagonal lines) is shown by the relationship T _a = T _M − T _L (1), and is a constant value because it has a uniform acceleration characteristic, but from another perspective, Since the signal l ₁ that sets the rate of change is constant, the acceleration torque T _a is constant. This means that if the moment of inertia is J, then from the relationship T _a = Jd _w /d _t ...(2) ∴ω=1/J∫T _adt ...(3), the angular velocity ω changes with respect to time t. This means that the acceleration torque T _a is constant and the output signal of the integrating circuit of the input limiting circuit 22 is proportional to the frequency reference f.
This is because the signal _l1 that sets the rate of change means the acceleration torque. In Figure 6, even though the overload torque during acceleration/deceleration determined by the power converter or electric motor is at the level of T _c , the acceleration/deceleration torque actually used is small, so there is a drawback that acceleration/deceleration time is long. It was hot.

Further, another example of the control circuit is shown in FIG. In the same figure, the difference from FIG. 3 is that the output of the V/F reference S2 is not directly used as the voltage reference v and the frequency reference f, but a signal S3 is obtained via a function generator 35, and the voltage is This is the point where a reference v and a frequency reference f are obtained. The characteristics of the function generator 35 are shown in FIG. 8, and a signal S3 is obtained by approximating a parabola with three polygonal lines for the signal S2. This relationship is the same for the time t-signal S3 relationship, so constant acceleration characteristics are obtained between times _t0 - _t1 , _t1 - _t2 , and _t2 - _t3, respectively. FIG. 9 shows the generated torque T _M of the induction motor 13, the load torque T _L , and the acceleration torque T _a indicated by diagonal lines at this time. Compared to FIG. 6, the utilization rate of the acceleration torque is good, but it is still insufficient, and the disadvantage is that the circuit becomes quite complex in order to increase the accuracy of the approximation of the function generator 35 in order to improve the utilization rate. It was hot.

The present invention has been made based on the above circumstances, and calculates the amount related to the acceleration/deceleration torque from the acceleration overload characteristic curve of the power conversion device or the electric motor and the characteristic curve of the load device, and adjusts the acceleration/deceleration torque according to this amount. An object of the present invention is to provide a control device for an electric motor that adjusts speed.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 10 is a block diagram showing one embodiment of the present invention. In this figure, the difference from Figure 3 is that the signals l ₁ and 1 are used to set a constant acceleration/deceleration rate.
Instead of using l ₂ , a function generating circuit 36 generates a signal l ₃ approximating the load torque with square-law characteristics using the frequency reference f as an input, and a signal l of the overload amount T _c during acceleration/deceleration determined by the power converter or electric motor. ₄ , a subtractor 38 which inputs signals _l3 and _l4 and generates signal _l5 representing the amount of acceleration torque during acceleration;
an adder 39 that adds the signal _l3 and the signal _l4 as input;
This signal is inverted to signal the amount of deceleration torque during deceleration.
The point is that it includes an inverting circuit 40 that generates _l6 . FIG. 11 is a detailed diagram of the function generating circuit 36, which generates a relationship between the input frequency reference f and the output signal _l3 in which the square characteristic is approximated by three polygonal lines. In the figure, as the potential of the frequency reference f increases, the resistor 69, setting device 70-diode 7
1-Resistor 72 and setting device 73-Diode 74
- The input current increases in the path of resistor 75, and the output signal of operational amplifier 77 increases. This signal is inverted by an operational amplifier 80 using the gains of resistors 78 and 79 to obtain an output signal _l3 at a (+) potential. As a result, the signal l ₃ obtained becomes the polygonal line shown in FIG. In other words, during the OA period, the circuits of the setting device 70, diode 71, and resistor 72 and setting device 73, diode 74, and resistor 75 are not activated. Also, between AB is setter 70 - diode 7
1-resistor 72 or setting device 73-diode 74-resistor 75, a predetermined circuit is activated. After B, all of the setting device 70, diode 71, and resistor 72 and setting device 73, diode 74, and resistor 75 are activated.

The figure shows the torque T _M generated by the induction motor 13 during acceleration, the load torque T _L , and the acceleration torque T _a indicated by diagonal lines. Strictly speaking, the torque T _M generated by the induction motor 13 becomes T _M = T _L + T _a , so it decreases by the torque between the polygonal line l ₃ and the load torque T _L , but
It is clear that this reduction is much smaller than in FIGS. 6 and 9. The fact that the shaded part shown in FIG. 12 can be the acceleration torque is because the acceleration torque component is calculated by (signal l ₅ )=(signal l ₄ )−(signal l ₃ ) in FIG. 10; It is clear from equations (2) and (3) that the acceleration rate is adjusted according to this amount, as it directly means the acceleration torque. FIG. 13 shows the generated torque T _M of the induction motor 13 during deceleration, the load torque T _L and diagonal lines ( ),
The deceleration torque T _d is shown in parentheses. In the same figure, since the load torque T _L also contributes to the deceleration torque,
T _d = T _M + T _L. Strictly speaking, since the load torque T _L is approximated by the polygonal line _l3 , the deceleration torque is calculated to be larger than the actual one, and the deceleration rate becomes a little faster, but this amount is not a problem. However, if you want to do it strictly, it is obvious that it is better to provide two types of setters 37, one for acceleration and one for deceleration, and set the overload amount for deceleration to a correspondingly low value. Note that FIG. 13 shows the time of deceleration, so when the frequency is high, the deceleration starts, and when the frequency becomes low and approaches the O point, the deceleration stops.

FIG. 14 shows another embodiment. The same figure is the 10th
The difference from the diagram is that a circuit similar to that shown in FIG. 10 is used only for acceleration, and the circuit shown in FIG. 3 is used for deceleration. This is adopted for the purpose of preventing excessive torque from being applied repeatedly in the normal use range where acceleration and deceleration is performed in a load device with a general square law characteristic, and the torque T _M generated by the induction motor 13 during deceleration. , the load torque T _L and the deceleration torque T _d indicated by diagonal lines ( ) and ( ) are shown in FIG.
In the figure, it is clear that the deceleration torque T _d is constant, as in the explanation of FIG. 6.

In the embodiment of FIG. 10, the overload amount setting device 3
By using 7 as a function generator which receives the frequency reference f as an input, an embodiment with other effects can be obtained. For example, if a function generator is used that reduces the amount of overload in a low frequency region, it is possible to overcome the property that semiconductor elements constituting an inverter circuit of a current source inverter have a reduced current carrying capacity in a low frequency region. In other words, in the low frequency range, the semiconductor elements that make up the power converter have a longer firing period than in the high frequency range.
The amount of heat generated internally increases and the junction temperature rises to a high level. Junction temperature accelerates the deterioration of semiconductor devices. Therefore, in order to lower the junction temperature, it is sufficient to provide a function generator that reduces the current carrying capacity. Furthermore, when passing a frequency that matches the resonance frequency of the machine, it is possible to quickly pass through that frequency by using a function generator that increases the amount of overload near that frequency.

The above explanation has been based on the combination of a current source inverter and an induction motor, but since the important point of this invention is to determine the acceleration/deceleration rate according to the overload curve of the power converter or motor, It is clear that the invention can also be applied to combinations of thyristor motor control devices, synchronous motors, etc.

As described above, according to the electric motor control device of the present invention, the acceleration/deceleration rate is adjusted by determining the amount related to acceleration/deceleration from the acceleration/deceleration overload characteristic curve of the power conversion device or the electric motor and the characteristic curve of the load device. By doing so, you can get the following effects:

(1) When approximating load torque using a function generator, even if the approximation curve is somewhat rough, it approximates the torque itself, so a very simple circuit can sufficiently generate the acceleration/deceleration torque of a power converter or electric motor. It can be used for.

(2) Various inconveniences that occur during acceleration and deceleration can be eliminated by setting the overload characteristic curve in consideration of not only the conditions of the power converter or motor but also the conditions on the machine side.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the motor drive system, Fig. 2 is a detailed circuit diagram of the power conversion device, Fig. 3 is a block diagram of a conventional motor control device, and Fig. 4 is a detailed diagram of the input limiting circuit in Fig. 3. Figures 5 and 6 are acceleration characteristic diagrams of the conventional system, Figure 7 is a block diagram of another conventional control device, and Figures 8 and 9 are the acceleration characteristics of the conventional system.
Figure 10 is a block diagram showing an embodiment of the present invention, Figure 11 is a detailed circuit diagram of a function generator, Figures 12 and 13 are acceleration and deceleration diagrams of the present invention. FIG. 14 is a block diagram showing another embodiment of the present invention, and FIG. 15 is a deceleration characteristic diagram of the control device shown in FIG. 14. 11...AC power supply, 12...Current source inverter, 1
3...Induction motor, 14...Load device, 21, 23,
24, 37, 70, 73... Setting device, 22... Input limiting circuit, 25, 28... Comparator, 26... Voltage control circuit, 27, 31... Transformer, 29... Current control circuit,
30... Current transformer, 32... Phase control circuit, 33... Oscillator, 34... Ring counter, 35, 36... Function generator, 38... Subtractor, 39... Adder, 40... Inverting circuit, 51, 52, 54, 55, 57, 63, 6
4,65,66,67,68,69,72,7
5, 76, 78, 79...Resistor, 53, 56, 5
9, 77, 80... operational amplifier, 58... capacitor, 60... absolute value conversion circuit, 61, 62... limiter, 71, 74... diode, 121... rectifier,
122...DC reactor, 123...Inverter circuit.

Claims (1)

[Scope of Claims] 1. Drives an electric motor to which a load device is connected, comprising a rectifying means for rectifying alternating current power and an inverter means for converting the direct current power rectified by the rectifying means into alternating current power of a predetermined frequency. a power conversion device that sets the speed of the electric motor;
an input limiting means that receives the output of the setting device as an input and outputs a voltage reference and a frequency reference; a voltage controlling means that controls the output voltage of the power converter based on the voltage reference of the input limiting means; and a frequency control means for controlling the frequency of the inverter means of the power converter based on a frequency reference of the means, wherein the acceleration/deceleration rate of the electric motor is adjusted according to the frequency reference when accelerating or decelerating the electric motor. 1. A control device for an electric motor, characterized in that a function generating means for adjustment is provided, and the output of the function generating means is used as an input to an input limiting means during acceleration and deceleration. 2. The electric motor control device according to claim 1, wherein the input to the input limiting means is determined from an overload characteristic curve during acceleration/deceleration of the power conversion device or the electric motor and a characteristic curve of a load device. 3. When the characteristic curve of the load device is a square load characteristic, the square characteristic is approximated by a polygonal line, and the input from this polygonal line approximation curve and the acceleration/deceleration overload characteristic curve of the power converter or electric motor is input to the input limiting means. The electric motor control device according to claim 2, characterized in that the electric motor control device requires the following.